Adding electrical relays, to save old stuff

[Dale]

Hi All,
Sorry I'm so slow on the uptake, it's been several days since I was asked to start a new thread regarding this topic. I did go to the suggested web site and print out the article about adding relays to the headlight circuit. It is very informative and may explain why my 100 watt halogen bulbs don't seer retinas like I had hoped, even though my TR7 has relays out the gazoo. I would like to add relays to the turn signals on my J-H. Those switches are available on E-bay, but the starting bid is like a gazillion dollars. Any particular problems with adding relays to signals? And of course anything you'd like to post about this is welcomed.

 

[Geo Hahn]

I bought about 10 30-amp relays from these guys (about a buck apiece IIRC):

https://www.goldmine-elec-products.com/products.asp?dept=1118

...and have used them on a variety of applications including the headlamps on the TR4.

They do not have the exact ones I got (they sell overstock & discontinued stuff) but they surely have something similar.

 

[TR3driver]

Good link, Geo, Thanks! I got mine on eBay for a bit more money, but including a plug and short harness, Eg:
https://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190312347666

Dale, your original turn signal flasher probably requires some minimum current for correct operation. Generally the OEM flasher is matched to the number of filaments on the car; so it flashes funny (either slow or fast) if a bulb burns out. But even "heavy duty" flashers generally require some miminum current for correct operation. I don't know if a pair of relay coils would draw enough current or not. You may need to find a flasher that is advertised to work with LED lamps.

You'll also need to look at how the indicator on the dash works. I don't know anything about JH in particular; but some cars with a single bulb assume that the actual turn signals are lower resistance than the bulb in the dash. That won't be true if you replace the turn signals with relays.

 

[JodyFKerr]

Dale,

Funny you should mention the JH. I was reading about the relays and such and started wondering how to upgrade/update the JH wiring harness to intelligently add relays (for example, the headlight switches are $expensive$ and crappy, a relay would save a lot of those).

I'm sandblasting Studebaker bits at the moment, but perhaps we can work through the relays on the JH together.

Jody

 

[70herald]

Turn signals really don't draw alot of current. I find it hard to believe that adding a relay would make much of a difference in the lifespan of the switch.

 

[71MKIV]

There are electronic flashers, usually used when low current LED lights are used, that are timers rather than current sensors.

I have seen them on superbrightLEDS.com. There are probably places to get them cheaper, maybe even the flaps.

Yea, I don't see the reason for relays in the turn signal circuits. To me that would just add complexity. Headlamp circuit definitly.

 

[dklawson]

I have relays for the headlights on the Mini, and I have added one to the horn circuit, but I have never thought about adding relays to the turn signals.

You don't necessarily have to use an LED specific electronic flasher. You could use the generic Tridon EL12 or EL13 (2 and 3 terminal respectively) type electronic flasher from the local parts store. They run around $10. That would allow you to add the signal relays if you want to, but you will be sacrificing what Randall pointed out... the signals won't change their flash rate when bulbs blow.

I've had signal switches mechanically fail but I've never seen the contacts wear out.

 

[TR3driver]

You could use the generic Tridon EL12 or EL13 (2 and 3 terminal respectively) type electronic flasher from the local parts store.

Worth a try, certainly, but I'm dubious. The EL13 doesn't actually use semiconductors; it's an electro-magnetic relay and a capacitor. It still relies on the load to draw enough current to pull in the relay inside the flasher; meaning it has some minimum current draw for proper operation. If the only load is another relay, it's probably not going to work. (I assume the same applies to an EL12, but I've not had one of them apart.)

The problem is that a standard 2 or 3 terminal flasher has no connection to ground; so it has to get it's power in series with the load. The LED flashers require a connection to ground so they get their power directly.

 

[dklawson]

Good points. I have seen the EL13 work with two lamps (of four) disconnected. You're probably right that a single relay won't pull anywhere near as much current as two lights. Maybe that LED flasher would be the thing to use.

 

[Dale]

Hi All,
Again I apologize for getting back in so late. As the turn signal and dimmer switches are so often on the same stalk, it would make sense to save the dimmer switch and avoid replacing both. I can see why the turn switch probably wouldn't be as needful of relay protection. Am going out to do a little shopping, and will browse at the Auto-Zone for relays. If I install 30 amp relays, what size fuses should I protect the added circuit with?

 

[TR3driver]

Choose the fuse according to the load; then make both the wiring and the relays at least that size (preferably larger). Typical turn signal filaments draw around 2.2 amps per filament or a bit less, so at least a 5 amp fuse (SAE or ISO rating system, double that for BS/Lucas rating system) for two filaments. I'd go 10 amps to be on the safe side (the larger fuse will also have a slightly lower voltage drop). That means 18 AWG wire would be adequate, but personally I'd go with 14.

Obviously a 30 amp relay is overkill in this case, but it won't hurt anything at all.

 

[Geo Hahn]

Good luck at Autozone. When I tried to buy relays there (and another chain store) they wanted to know 'What's it for?'. Unless I could specifically say it was (for example) for the headlamps on an 94 Accord they couldn't help me.

If you have a CarQuest or such available they may be more useful. The one I went to still used a paper catalog and let me browse for what I wanted.

 

[Dale]

The local Auto Zone had 2 relays in stock 12V, 30 Amp, 4 terminals, 30-85-86-87. Sounds like what I need, but I didn't buy them as I didn't know if the price was right. $5.99 each. What ya think?

 

[Dale]

I am thinking 14 gauge from the alternator positive terminal to the relays, with 10 Amp in line fuses. I will inspect the stock wiring and reuse it from the relays to the headlights and from the dash switches to the relays. The headlights are currently working OK, so employing the old wires on the low power side of the relays should be OK. OK? Your thoughts?

 

[TR3driver]

Those relays should work fine, if they are decent quality. And $5.99 is reasonable; probably not worth the hassle of trying to mail order them to save a dollar or two.

I'm a little confused over the rest of it, though. Are you still talking about relays for turn signals on your JH? Or for those 100w headlights on the TR7?

Headlights are kind of a special case; you really, really don't want those suckers going out suddenly. BTDT. Dan Masters recommends using no fuses or circuit breakers at all, and I agree that he has a point. If you do want to use fuses, then I would suggest a separate fuse for each filament (so that a single fuse failure won't cut off both lights). That means 4 relays if you want to protect the wires to the relays as well.

If you are using a separate wire for each filament, then 14 AWG is OK. If not, I'd go larger. (In fact, I'd go larger anyway; I used 10 AWG on the Stag.)

Old wires on the low power side sounds fine; but from the relays out to the headlights is not the low power side, especially with 100 watt headlights. It's your choice of course, the stock wires won't burn up or anything; but larger wires will deliver more voltage under load, meaning more light on the road. And that's the point, right?

 

[Dale]

Sorry I wasn't more precise. I am only going to deal with the J-H headlights at this time. They are stock Lucas units, I'm guessing 55 watts. The relays are primarily to save the original dimmer switch, which is in unit with the turn signal switch. The 100 watt bulbs on the 7 will have to get by until I can rewire with heavier wire. The TR7 already has relays for Hi and Low beam in addition to relays on the retractable headlight motors. I suspect that the wiring rather than the relays is the reason the 100 watt bulbs don't perform as expected. The J-H headlights are currently working well in terms of brightness. In fact, when we were driving at night last spring, I bothered most oncoming traffic with my low beams as they were seriously out of adjustment. That is why I think I can get by with using the existing wires from the relays to the lights. I am in a quandary as to fusing the relays. I had been assuming that fuses were good and burned up wiring harnesses were bad. I understand that driving in sudden darkness could be disconcerting at best. With a separate fuse for high beam and low beam I will have to rely on my quick wits and cat like reflexes to switch beams in the event of a failure. ( I hear the snickers) I guess the relays themselves would provide some circuit protection as the headlight circuit will be isolated from the main harness by them. Well sort of. My head is starting to hurt so I'm going to rest on it a bit. I do appreciate the input and welcome anything further you might have.

 

[TR3driver]

On my TR3A, I had a unit that incorporated two relays and two fuses in a metal box (originally sold as an upgrade for a Model A Ford I believe

). Going down a mountain rather over the speed limit one very dark night, the headlights just went out! As you say, I just hit the high beams and all was well; but the pucker factor was high. I'm glad I wasn't going around a narrow mountain curve at the time, cuz there wasn't any road at all when the lights went out.

I'm a little dense sometimes, it happened twice more (fortunately when it wasn't so dark) before I finally realized that the clips for the fuse had corroded slightly, just enough to get warm after long operation with the headlights on. The heat would melt the solder inside the fuse, resulting in a fuse that didn't appear to be blown but would not conduct. I assumed first it was just a bad fuse, then a bad box of fuses; but the third fuse was from a different box. Buffing the clips up a bit with a ScotchBrite and smearing a little silicone grease solved the problem.

One solution might be to use a "fusible link" instead of a fuse. A fusible link is just a section of smaller diameter wire, with high temperature insulation. It's a lot less fragile than a fuse (and takes longer to blow) but should protect the wiring if there is a short.
https://www.madelectrical.com/catalog/fusible-link.shtml